Inductive charging (also known as “wireless charging”) uses an electromagnetic field to transfer energy between two devices. For example, energy may be sent from a charging station through an inductive coupling to a portable device, which can then use that energy to charge batteries or operate the device. Inductive charging can be used to charge batteries in small devices like mobile phones or in larger devices like electric vehicles.
An inductive charger typically utilizes a primary inductor or coil to create an alternating electromagnetic field from within a charging base station. A device with a secondary inductor or coil is positioned close to the charging base station so that the field generated by the primary inductor couples to the secondary inductor. Thus, the secondary inductor experiences changing field strengths (or signal strengths) as it is moved farther or closer to the primary inductor. The secondary inductor takes power from the electromagnetic field based on the received signal strength and converts it back into electrical current that can be used to charge a battery. Since there is no direct or wired connection in an induction charging system, the electronics may be sealed for protection from the elements and durability is improved since there is no need to plug and unplug electrical connectors.
During a typical charging process, the user simply places the device to be charged on a charging surface of a charging station. The charging station detects the presence of the device and begins a charging process that includes determining device identification and configuration parameters. Once the configuration is completed, an energy transfer is performed through an inductive coupling until the device signals that battery charging has completed, or until the device is removed from the charging surface. A detailed description of an inductive charging system and its operation is disclosed in a document entitled “System Description Wireless Power Transfer” version 1.1.2 published by the Wireless Power Consortium in June 2013, the contents of which are incorporated by reference herein.
The rate of energy transfer can greatly affect the length of time necessary to charge a device's battery. The signal strength determined from the relative positions of the primary and secondary inductors determines the overall rate of energy transfer. A quality of charge (QoC) metric can be determined that characterizes the overall power transfer from the charging station to the charge receiving device. A higher QoC metric indicates higher efficiency that will result in shorter battery charge time and a lower QoC metric indicates lower efficiency that results in longer battery charge time.
In practice, this means that a device's placement on a charging surface relative to the primary inductor affects the signal strength experienced by the charging device and therefore the QoC metric. It is desirable to place a device on the charging surface such that the highest or optimum QoC metric is achieved so that battery charge times can be reduced or minimized.
Conventional systems may provide only a simple on/off indicator to indicate whether or not a device's battery is charging. Unfortunately, an on/off charging indicator provides no information to the user about the QoC. As a result, a device user may not know anything about the rate of energy transfer to the receiving device or the overall battery charge time.
Therefore, it would be desirable to have a mechanism that quickly determines a QoC metric during induction charging, and provides notification of the QoC metric to a user to allow the user to reposition a charge receiving device on the charging surface to increase the QoC metric and thereby increase energy transfer and decrease or minimize battery charge time.